The present invention concerns a method for the recovery of pentaerythritol from residual mixtures resulting from the synthesis of pentaerythritol itself, said residual mixtures containing, together with other byproducts, greater amounts of formals.
It is known from Italian Patent Publication 21222 A/78, assigned to Montedison, S.p.A., Milan, Italy, to synthesize pentaerythritol by multiple aldolic condensation of acetaldehyde with formaldehyde and by successive disproportioning, in the presence of aqueous sodium hydroxide. It is also known to crystallize the greatest part of pentaerythritol from the synthesis mother liquor, by then isolating, separately from said mother liquor, a non-negligible amount of pentaerythritol (not previously precipitated), almost stoichiometric quantities of sodium formate and residual mixtures containing (besides minor amounts of pentaerythritol, formate and other byproducts) considerable amounts of formals. Said residual mixtures may be isolated as an alcoholic solution (obtainable, for instance, according to the Italian Patent Publication hereinabove or according to Japanese Patent Publication No. 15 566/77) by means of an extraction of the formals and of the other undesired byproducts from the synthesis mother liquor, using an alcohol as extracting agent. Said Japanese Publication teaches, moreover, to remove the alcohol by means of an evaporation and to hydrolize the formals with an acid, in an aqueous solution.
Operating in this way, the recovery yields are not, however, very great; besides that, the physical separation of the pentaerythritol from the aqueous medium thus obtained proves rather troublesome.